Mumblecore is, at heart, about small defining moments: the affair that didn’t quite happen, the conversation that shouldn’t have taken place, the missed opportunity and the lost chance. In “Humpday,” which was released in July, Joshua Leonard and Mark Duplass play former college buddies who dare each other to make a gay porno starring themselves. Duplass’s character is married and is afraid he has lost all bohemian impulses, while Leonard’s character has been restlessly roaming the globe. These two straight guys are afraid of being conventional, staid, old.